Electricity (KWH) Meter Spins Back, but stops counting down.

[kolbep]

So here is a question for all you clued up people,
Say this person has this specific KWH meter,


and they also have a 6KVA PV System.

Their PV System is set to feed in Everything it generates, that is not being consumed locally.
This Meter Spins it's disc backwards, and the Counter Decrements as the PV System backfeeds to the grid.

But then it gets to a round figure (27860 Kwh), in the morning, after which the disc still spins backwards, but the counter does not decrement any more past that.

Turned off the PV system, and ran it up to 27879 Kwh (using just the grid), Then again when running on the PV, it dropped down to 27870 (at Midday), disc still continued to spin backwards even though the numbers were no longer decrementing.

I even hooked up an energy meter to the Grid side, as well as the PV side, and it showed a net export to the grid (several KWH higher than was consumed), so it should have gone down even more
 
I have heard that some of the Meters like this have a ratchet, that stops the disc from rotating backwards,
but I was wondering if there are meters (maybe like this one), that have a stop of some kind that stops it decrementing past 0..
 
Any Ideas?

Thanks

[DenzilPenberthy]

I would guess that there is a ratchet mechanism that stops the counter decrementing.   The disc drives the least significant digit which then drives the others via 10:1 gear ratios.

Probably the additional friction from the ratchet mechanism might stall the disc if placed directly on the least significant digit (or on the disc itself) but due to the gearing ratio, it works much more reliably on a higher digit where more torque is available.  (and the designers figured that was an ok compromise to put it on the 10's counter)

Pure speculation though, I've never taken one of these apart.

[coppice]

Some of the mechanical counters used in these types of meter cannot kick the digits backwards, others can. I don't think this was planned as a tamper protection. Its just a natural consequence of how the mechanism works. The last digit doesn't have the same "kick once per turn" mechanism as all the other digits, and has no problems rotating forwards or backwards.

[Macbeth]

I remember those old meters could be tricked into spinning backwards and reversing count. Case in point - my aunty back in the '80s had some dodgy contraption fitted by a dodgy electrician and hidden in the meter cupboard that when switched on would run it backwards. She accidentally left it switched on when she went on holiday only to return to find her meter reading was months behind her last bill and the leccy man was coming to read the meter soon... Cue panic stations and her borrowing electric radiators, bar fires to load the sockets in every room in the house, all lights on, washing machine and dryer on, hoover running, TVs, radios, the lot for 24/7 for a couple of weeks 

I think bigclive featured this electricity meter hack in one of his videos...

ETA:

[vodka]

I don't think this was planned as a tamper protection

You are wrong , the ratchet is a measure anti-fraud.

The last digit doesn't have the same "kick once per turn" mechanism as all the other digits, and has no problems rotating forwards or backwards.

Carefulness,althought the the digits don't rotate backward  with the digits meters, you may have  a problem with the electrical corporation , because the corporation  will interpret as a possible fail fraud and you
will sanction with a cut-off from the grid plus penalty fee(at my country between 3000-6000€)and if the infringement is very  serious a criminal complaint

[coppice]

I don't think this was planned as a tamper protection

You are wrong , the ratchet is a measure anti-fraud.

You might be right. These days anti-tamper techniques are becoming a much bigger issue in utility meters for electricity, water, gas and heat. Most meters shipping today are not hard to tamper with. A powerful magnetic on the case of most utility meters will mess them up badly, and the magnetic is "self adhesive". . When someone comes to read the meter its easy to pull the magnet off - just be real careful of your fingers. An electronic meter can easily log these activities, but customers can simply complain that the hardware must be faulty. Proving its not isn't easy. Perhaps constant monitoring through smart grid networks will deter this kind of behaviour.

[SeanB]

It is an anti rollback feature, simply done by having a modified tens digit counter dog, so it was easy to retrofit to the multi thousands of these meters that are around. That was done because unscrupulous people discovered that you could make the meter run backwards simply by connecting a big welder to the mains, which caused a massive out of phase current that made the meter run backwards. Started in the 1980's with the modification done as these meters came into the workshops in the 10-20 year calibration check cycle.

A lot cheaper to simply undo the front face, undo the counter and cut the centre rod ( it is crimped both ends to hold it in place) then dismantle partly and replace the one digit, then push back the rod and slip the white digit back on, and then crimp the rod end again to lock it. Then you put it in a calibration fixture along with around 20 others and simply run a 0.5 hour calibration current through it and see they all count the same number up and agree with the calibrated control meter. 99% will still be as accurate as the day they were made.

[mmagin]

So, where I live, you're supposed to have utility approval for grid-connected PV systems, and then they switch you over to a net metering arrangement (for a one year period).

So, uh, it makes me think that either the utility doesn't know in this case or they're too lazy to deploy a proper meter for net metering.

[SeanB]

No, Eskom is not exactly moving at anything that could be called "fast" ( they make the term Glacial seem positively speedy) in allowing any form of feed in tariff, or of allowing Independent Power Producers to feed small scale power into the grid. They are protecting the monopoly they have over power generation, despite there being numerous requests to allow it. The only one allowing it in any way is the Cape Town Metro, which is it's own power distributor, and which would like extra power to reduce loading on the long feeder lines to it.

Thus most solar installations are forced into either installing battery storage, or of not being paid for the power fed back, or for some of the meters actually being billed for this power, as the meter does not discriminate on power feed direction, just accumulated kWh of power, mostly the modern smart meters.

[Macbeth]

No wonder Martin Lorton escaped S.A.